1. Field of the Invention
The present invention relates to a vacuum-sealing-type flexible-film primary battery and a method of manufacturing the same, and more specifically, to a vacuum-sealing-type flexible-film primary battery, which uses a pouch as a collector substrate and employs a non-metal terminal technique, and a method of manufacturing the primary battery.
2. Discussion of Related Art
In recent years, a vast amount of research has been conducted on active radio frequency identification (RFID) tag technology. It is expected that the active RFID tag technology, which has a far-reaching influence on a wide variety of fields including digital TVs, home networks, and intelligent robots, will be highlighted as the next-generation essential industry that will surpass current code division multiple access (CDMA) technology. In other words, unlike a conventional passive technique of reading information stored in a tag using a reader, the active RFID tag technology may not only lead to a remarkable increase in a tag recognition distance but also enable sensing of information on objects and environments around a tag. Ultimately, it is expected that the active RFID tag technology will expand an information flow region from communication between a human being and an object via networking to communication between objects.
In order to drive an RFID tag, it is important to secure an internal power source completely separated from a reader. In this case, the internal power source may use a power device appropriate for the RFID tag, which is compact and lightweight and has a long lifespan. Also, a tag coverage may be expanded from a pallet level corresponding to a load transportation unit to an item level corresponding to each product. Considering that an applied tag is discarded after its original object is achieved, it would be most appropriate to apply a primary battery to the tag. Up to now, a film-type primary battery has partially been applied to an RFID tag and recognized as a useful power device.
Meanwhile, more attention has lately been paid to flexible devices. Flexible ubiquitous terminals, such as scroll-type displays, e-papers, flexible liquid crystal displays (LCDs), flexible organic light emitting diodes (OLEDs), and wearable personal computers (PCs), have lately been put to practical use, so that the demand for flexible power devices has now begun to intensify.
Even if flexible power devices are repeatedly bent, the flexible power devices should be free from any cracks in an electrode plate, separation between an electrode and an electrolyte, or separation between a collector and the electrode. Thus, to ductilize the collector, the collector should be formed of a material which is capable of improving the ductility of the collector, rather than a metal. Also, the electrode plate should be easily formed on the ductilized collector, and a completed battery should be structurally stable to effectively resist to bending or folding. Moreover, manufacture of flexible power devices should be simple using equipment that facilitates performing sequential processes.
A conventional film-type primary battery is a film-type 1.5V manganese (Mn) battery in which an electrode and an electrolyte have the same configuration as a typical dry battery and a container formed of a polyethylene terephthalate (PET) package material is used instead of a cylindrical can and laminated as a film type. However, although most polymer films may drop transmittance of moisture in a gas or air to a predetermined level or lower, it is impossible to completely cut off the transmittance of moisture in the gas or air. In the long run, this may result in leakage or dryness of the electrolyte contained in a cell. In addition, since most polymer films, except a polyolefin film, have low corrosion resistances to strong acids or strong bases, a direct contact of the polymer films with the electrolyte over a long period may lead to corrosion of the polymer films. These problems may detrimentally affect the durability, retention periods, and lifespans of film-type batteries, thereby greatly reducing the performances thereof.
Furthermore, as the function of tags evolves from a battery sustaining function into a sensor function, a sensor may be mounted on a tag so that a driving voltage of the tag may be increased to 3V. Thus, when conventional 1.5V film-type primary batteries are mounted on a tag, the 1.5V film-type primary batteries should be necessarily connected in series so that the volume of the batteries can be doubled in a limited space, thus reducing an energy density.
Meanwhile, in the field of lithium secondary batteries, a pouch formed of a sealed packing material has been proposed to increase a durability, a retention period and a lifespan. A typical pouch has a triple composite structure, which includes an outer layer formed of a nylon-based polymer film, an inner layer formed of a polypropylene (PP) polymer film, and an intermediate layer formed of aluminum (Al) foil inserted therebetween. Thus, the pouch may have high flexibility and such an appropriate mechanical strength as to maintain a predetermined shape. The inner layer of the pouch, which is formed of PP, may be highly corrosion-resistive to strong acids or strong bases, insoluble in any solvent, and melt only with heat. The intermediate layer formed of Al foil may function as a perfect barrier layer. Thus, a typical pouch used for a lithium secondary battery may serve as a sealed packing material in a final battery manufacturing process.
By use of the pouch having perfect gas/liquid blocking characteristics and good vacuum sealing and thermal fusion characteristics, a film-type battery with good durability and performance may be manufactured using a simple process. To do this, a conductive carbon layer should be directly coated on the surface of the pouch. Since the PP inner layer of the pouch has a low surface energy and a hydrophobic characteristic, the PP inner layer have a poor wettability in an organic solvent and have a poor coating characteristic, so that it is impossible to directly coat the conductive carbon layer on the PP inner layer. This is because the coated conductive carbon layer may be easily delaminated after a drying process and further delaminated when impregnated with an electrolyte. This is due to the fact that the PP inner layer of the pouch is neither compatible nor miscible with any polar polymer that is currently known as a binder of an electrode slurry.
A polymer electrolyte used for manufacture of a film-type battery should have good long-term stability because the polymer electrolyte requires a long lifespan of at least two years. In other words, components of the polymer electrolyte should be neither dried nor hardened for at least two years if possible to prevent sudden performance degradation.
Unlike in a conventional method in which electrode plates are laminated and wound to fabricate a cell, a film-type battery is manufactured by simply laminating positive and negative plates between which an electrolyte layer is inserted, thus causing separation or bad contact between the electrode plate and the electrolyte layer.
Furthermore, a thin film-type battery needs to be manufactured using a simple low-cost process because of its own properties. However, conventional manufacture of primary and secondary batteries may involve welding a metal terminal to an electrode plate, which is coated on metal foil, using ultrasonic waves and vacuum-packing a laminated cell component including an electrolyte. Accordingly, when the conventional manufacture of batteries is applied to the thin film-type battery, it is difficult to overcome high process costs due to a multi-stage manufacturing process and reduce the unit cost of production of the film-type batteries.